Purification of aromatic nitriles



20 ordinary crude mixtures rarely contain over 50% vided it does not make the compound water 20 25 with ammonia in the presence of a catalyst, is 0., or concentrations above 5% are used, sub- 25 i Patented .Ian. 9, 1940 p i I I PURIFICATION OF AROP/XATIC NITRXLES Vito Giambalvo, Brooklyn, N. Y., assignor to Interchemical Corporation, New York, N. 51., a corporation of Ohio No Drawing. I Application August 23, 1938,

Serial No. 226,258

2 Claims. (Ci. 260 465) This invention relates to a method of separat phthalonitrile (M3. P. Mil-1&2" C.) was theoretical. ing pure aromatic di-nitriles from a mixture of The cold alkaline filtrate was then acidified aromatic imides and aromatic di-nitriles; 'with cold sulfuric acid. The precipitated Phthalonitrile (orthodicyanobenzene) and imide was filtered, and Washed acid free. The

6 other aromatic di-n'itriles may be prepared by use recovery was about 95% of theoretical, and I of the standard reaction for the production of have obtained recoveriesof about 98%. nitriles from acid amides, by treating phthal- By my method,'it is thus possible to obtain amide or phthalimide with ammonia, preferably almost completely pure phthalonitrile, with subin the vapor phase, in the presence of a catalyst. stantially no loss of the original starting product.

19 The crude reaction product has been purified in The method may likewise be used with other 10 the past by stirring the broken up reaction prodaromatic di-nitriles. Thus, I have reacted naphuct with caustic soda solution to dissolve the .thalimide and ammonia in the vapor phase at unconverted phthalimide and other reaction 458 C. over conventional catalysts, to obtain 2. products, and the phthalonitrile has been recrude reaction mixture, which was then treated covered by filtration. The difficulty with this as above, with substantially the same yield and 15 method is that the caustic soda hydrolyzes the results. phthalimide to phthalic acid, so that recoveries Substituted aromatic dinitriles may also be of phthalimide are poor. This materially inprepared, provided the substituent is not a group creases the cost of the phthalonitrile, since the which reacts readily with caustic soda, and prore'r W i of phthalonitrile. soluble. Thus, halogenated di-nitriles can be I have discovered that if acrude mixture of purified by my method, but hydroxy substituted phthalonitrile and phthalimide, such as is obproducts cannot. Y

tained by reacting phthalamide or phthalimide As indicated above, if temperatures higher than treated with very cold, Very dilute caustic alkali, stantial hydrolysis of the imide to the acid takes such as sodium, or potassium hydroxide, the place, the rate of conversion increasing with inphthalimide may be recovered as such without creasing concentration and temperature. The hydrolysis, while the phthalonitrile remains beacidulation of the filtrate should, of course, be

hind as an insoluble precipitate. carried out as soon as possible, in order to mini- 30 I have found that the caustic alkali should be mize the risk of hydrolysis. used in concentration of 5% or lower, and the WhatI claim is:

treatment of the crude mixture must take place I 1. The method of separating a mixture of an at 5 C. or lower. aromatic imide and a waterand dilute alkali- As a typical example of my invention, I reinsoluble aromatic di-nitrile, which comprises P acted the vapors obtained by heating 164 pounds dissolving the imide in an aqueous caustic alkali of phthalamide with 30'pounds of gaseous am solution of no greater than 5% concentration, at monia, carrying the mixture over a catalyst a tempera u e 110% abOVe Separating t comprising diatomaceous earth, maintaining the solid di-nitrile from the irnide solution, and pre- 4o reaction zone at 400 C. The crude mixture p ing the imide. 4O

weighing 137 pounds resulting contained about The meme-d of separating xture of 50% phthalonitrile, and about 50% of phthaliphthalimide and phthalonitrile', which comprises mide, slightly contaminated with other reaction d s v g t e imide in an aqueous caustic alkali products. This mixture was broken up, and solution of no greater than 5% concentration, at

5 treated with 950 pounds of a 2% caustic soda soa temperature not above 5 C., separating the lution at 1 C., while stirring was continued solid di-nitrile from the imide solution, and pro for ten minutes, and the slurry was filtered and Cipitaliing the imidewashed alkali free with water. Recovery of the VITO GIAiMBALVO. 

